In focal plane shutters of the prior art, curtains are positioned with edges thereof in spaced relation to define a slit which is moved through an exposure region to expose film to a transmitted image. One prior type of shutter has a drive which includes a drive motor, clutches, brakes, cams, a differential gearing assembly and springs. In a winding part of a cycle, the drive operates to close the slit and to wind the springs. In an exposure part of the cycle, the differential gearing is used to position the curtains to provide an open slit and then the springs are released to move the slit across the exposure region with the velocity of movement being controlled by the cams and associated friction means.
Another prior type of shutter includes clutches operable to drive curtains from a continuously operating electrical motor and a differential gearing assembly and braking arrangement are provided which permits one curtain to be braked while driving the other, to adjust slit width prior to an exposure operation. This type of shutter may be made to operate in either direction, exposures being made in both directions of movement of the curtains.
Such prior types of shutters have required careful construction with precision parts and have been somewhat expensive as a result. However, the users thereof have generally been very satisfied with their performance and reliability.